Method and device for ascertaining a minimum value for the friction coefficient of a road segment

Abstract

A method for ascertaining a minimum value for the friction coefficient of a road segment, in which at least one movement variable of a second vehicle, which characterizes the vehicle movement, is ascertained with the aid of a surroundings sensor system contained in a first vehicle; a minimum value for the friction coefficient of the road segment traveled by the second vehicle is ascertained on the basis of the at least one movement variable of the second vehicle; the spatial position of the first vehicle is ascertained; the relative position of the second vehicle with respect to the first vehicle is ascertained with the aid of the surroundings sensor system; the spatial position of the second vehicle is ascertained with the aid of the spatial position and the relative position of the first vehicle; the spatial position of the second vehicle and the minimum value are stored in a database.

What is claimed is: 
     
       1. A method comprising:
 ascertaining, by a control unit of a first vehicle and based on output obtained by the control unit from a surroundings sensor system of the first vehicle, a value of an acceleration or deceleration of a second vehicle; 
 ascertaining, by the control unit and based on a quotient calculated using the ascertained value of the acceleration or deceleration of the second vehicle and a constant, a respective friction coefficient value of a respective road segment traveled by the second vehicle during the ascertained acceleration or deceleration of the second vehicle; 
 ascertaining, by the control unit and based on output obtained by the control unit from a geolocation device, a spatial position of the first vehicle; 
 ascertaining, by the control unit and based on output obtained by the control unit from the surroundings sensor system, a relative position of the second vehicle with respect to the first vehicle; 
 ascertaining, by the control unit and based on the ascertained spatial position of the first vehicle and the ascertained relative position, a spatial position of the respective road segment; 
 causing, by the control unit and based on the ascertained spatial position of the respective road segment and the ascertained respective friction coefficient value, a friction coefficient map, which associates a plurality of friction coefficient values with respective ones of a plurality of positions of road segments, to be updated to identify the ascertained spatial position of the respective road segment in association with the ascertained respective friction coefficient value; and 
 controlling, by the control unit and based on one or more of the associations of the friction coefficient map, a vehicle system of the first vehicle. 
 
     
     
       2. The method as recited in  claim 1 , wherein:
 the quotient is ascertained as the respective friction coefficient value; 
 the quotient is of the longitudinal acceleration or deceleration divided by the constant; and 
 the constant is a value of gravitational acceleration. 
 
     
     
       3. The method as recited in  claim 1 , wherein the surroundings sensor system includes at least one of a radar sensor system and a video sensor system. 
     
     
       4. The method as recited in  claim 1 , wherein the geolocation device includes or is a part of a satellite-based positioning system. 
     
     
       5. The method as recited in  claim 1 , wherein the relative position of the second vehicle is ascertained simultaneously or virtually simultaneously with the ascertainment of the respective friction coefficient value of the respective road segment traveled by the second vehicle during the ascertained acceleration or deceleration of the second vehicle. 
     
     
       6. The method as recited in  claim 1 , wherein the friction coefficient map is maintained on a vehicle-external server that wirelessly transmits information of the friction coefficient map to the first vehicle, and the causing of the friction coefficient map to be updated includes wirelessly transmitting to the server the ascertained spatial position of the respective road segment and the ascertained respective friction coefficient value. 
     
     
       7. A control unit of a first vehicle, the control unit storing a computer program that the control unit is configured to execute and that, when executed by the control unit, causes the control unit to perform a method, the method comprising:
 ascertaining, based on output obtained by the control unit from a surroundings sensor system of the first vehicle, a value of an acceleration or deceleration of a second vehicle; 
 ascertaining, based on a quotient calculated using the ascertained value of the acceleration or deceleration of the second vehicle and a constant, a respective friction coefficient value of a respective road segment traveled by the second vehicle during the ascertained acceleration or deceleration of the second vehicle; 
 ascertaining, based on output obtained by the control unit from a geolocation device, a spatial position of the first vehicle; 
 ascertaining, based on output obtained by the control unit from the surroundings sensor system, a relative position of the second vehicle with respect to the first vehicle; 
 ascertaining, based on the ascertained spatial position of the first vehicle and the ascertained relative position, a spatial position of the respective road segment; 
 causing, based on the ascertained spatial position of the respective road segment and the ascertained respective friction coefficient value, a friction coefficient map, which associates a plurality of friction coefficient values with respective ones of a plurality of positions of road segments, to be updated to identify the ascertained spatial position of the respective road segment in association with the ascertained respective friction coefficient value; and 
 controlling a vehicle system of the first vehicle based on one or more of the associations of the friction coefficient map. 
 
     
     
       8. A non-transitory computer-readable medium on which are stored instructions that are executable by a control unit of a first vehicle and that, when executed by the control unit, cause the control unit to perform a method, the method comprising:
 ascertaining, based on output obtained by the control unit from a surroundings sensor system of the first vehicle, a value of an acceleration or deceleration of a second vehicle; 
 ascertaining, based on a quotient calculated using the ascertained value of the acceleration or deceleration of the second vehicle and a constant, a respective friction coefficient value of a respective road segment traveled by the second vehicle during the ascertained acceleration or deceleration of the second vehicle; 
 ascertaining, based on output obtained by the control unit from a geolocation device, a spatial position of the first vehicle; 
 ascertaining, based on output obtained by the control unit from the surroundings sensor system, a relative position of the second vehicle with respect to the first vehicle; 
 ascertaining, based on the ascertained spatial position of the first vehicle and the ascertained relative position, a spatial position of the respective road segment; 
 causing, based on the ascertained spatial position of the respective road segment and the ascertained respective friction coefficient value, a friction coefficient map, which associates a plurality of friction coefficient values with respective ones of a plurality of positions of road segments, to be updated to identify the ascertained spatial position of the respective road segment in association with the ascertained respective friction coefficient value; and 
 controlling a vehicle system of the first vehicle based on one or more of the associations of the friction coefficient map.